The　dynamic　interactions　between　noble　metal　particles　and　reducible　metal-oxide　supports　can　depend　on　redox　reactions　with　ambient　gases.　Transmission　electron　microscopy　revealed　that　the　strong　metal-support　interaction　(SMSI)-induced　encapsulation　of　platinum　particles　on　titania　observed　under　reducing　conditions　is　lost　once　the　systemis　exposed　to　a　redox-reactive　environment　containing　oxygen　and　hydrogen　at　a　total　pressure　of　similar　to　1　bar.　Destabilization　of　the　metal-oxide　interface　and　redox-mediated　reconstructions　of　titania　lead　to　particle　dynamics　and　directed　particle　migration　that　depend　on　nanoparticle　orientation.　A　static　encapsulated　SMSI　state　was　reestablished　when　switching　back　to　purely　oxidizing　conditions.　This　work　highlights　the　difference　between　reactive　and　nonreactive　states　and　demonstrates　that　manifestations　of　the　metal-support　interaction　strongly　depend　on　the　chemical　environment.